16. Virology Introduction Flashcards
name a small virus
parvovirus
name a cylindrical virus
tobacco mosaic virus
why are viruses intracellular parasites
they have no capacity to perform any metabolism outside a host cell
viruses are obligate, what does this mean?
no replication cycle outside the host cell
how many virus particles on earth
10^23
why is taxonomy important in viruses
allows us to draw evolutionary conclusions on viruses and determine any ancestry
what did taxonomic classification of SARS-CoV2 show?
showed it to be a relative of SARS-CoV1
how did Linnaeus classify organisms
heirarchically: kingdom, phyla, class, order, family…
what does the Baltimore classify organisms on
what does this allow?
genome structure
allows us to group viruses that behave similarly in distinct groups
what are types 1-3 of the Baltimore classification system
type 1: dsDNA viruses
type 2: ssDNA viruses
type 3: dsRNA viruses
what are types 4-6 of the Baltimore classification system
type 4: positive sense ssRNA viruses
type 5: negative sense ssRNA viruses
type 6: ssRNA viruses (reverse transcriptase -> dsDNA)
what Baltimore class does Ebola belong to
class 5
what Baltimore class does SARS-CoV2 belong to
class 4
what is the …. of covid 19?
- species
- genus
- family
species: severe acute respiratory syndrome- related coranovirus
genus: betacoronavirus
family: coronaviridae
what is the opposite of filamentous
icosahedral
what does filamentous mean
forms filaments from protein subunits arranged in rings
give an example of a filamentous virus
tobacco mosaic virus = RNA genome surrounded by protein subunits
what does icosahedral structure mean?
complex crystalline structure that fit together to form a sphere (sort of like a football)
by what two ways can a virus be encapsulated
via capsid or lipid bilayer
in a bi-lipid envelope, where is the viral genome
sitting within the lipid bilayer
describe the envelope on Sindbis virus
have both a capsid and lipid bilayer which contain protruding proteins
spike proteins sit in the lipid bilayer, what does this induce
the immune response = antibodies
describe the envelope of SARS-CoV2?
does not have a capsid, just a lipid envelope
what surface proteins does SARS-CoV2 have?
spike glycoprotein, E protein and M protein
which surface protein Is the target of the vaccine
spike glycoprotein
what 2 proteins are embedded in the influenza envelope
neuraminidase
haemagluttinin
what is the function of neuraminidase
used in viral exit
what is the function of haemagglutinin
used in viral entry
briefly describe how the astra Zeneca vaccine works
- takes a chimp adenovirus vector and modified it to express SARS-CoV2 spike glycoprotein gene
- recombinant virus is manufactured into gene
- chimp virus is harmless to humans
how many kilo bases in the SARS-CoV2 genome, is this large?
30
this is very large
what is a polyprotein
large protein that is translated and cleaved into fragments - each fragment having its own function
describe SARS-CoV2 genome
30 kb
no polyprotien
each protein is transcribed separately
spike proteins bind to specifici plasma membrane receptors:
what does HIV bind to?
CD4 receptor on T-lymphocytes
spike proteins bind to specifici plasma membrane receptors:
what does infleunza bind to?
sialic acid on glycoproteins
spike proteins bind to specifici plasma membrane receptors:
what does rabies bind to?
acetylcholine receptor on nerve cells
spike proteins bind to specifici plasma membrane receptors:
what does SARS-CoV2 bind to?
angiotensin converting enzyme 2 found on pneumocytes
ACE2
how does Ebola virus enter cells?
using cholesterol transport protein
how are individuals with Niemann-pick disease resistant to ebola
lack cholesterol transport protein
- those who are homozygous = short life span & many symptoms
- those who are heterozygous = less harsh symptoms & EBOLA RESISTANCE
how do enveloped capsid viruses such as herpes simplex virus enter cells
receptors bind and the membrane fuses. here the contents are released into the cell and the capsid will dissolve and the viral genome will be released
how do bacteriophages release the genome into the cell
bind via the tail pin and inject the core into the cell - releasing the genome
how does HIV enter cells
binding to the variable region recruits a GPCR that conformationally changes, pulling the virus closer to the cell membrane
this results in a hydrophobic channel forming that allows the lipid bilayer to flow down the channel and the genome enters the cell
how do viruses leave the cell
virus produces many copies which are encapsulated in a. vesicle
vesicle fuses with the membrane creating its own lipid bilayer before leaving the cell, stealing part of the host cell lipid bilayer.
what does the capsid act to protect the virus from
harmful environmental factors such as UV
give an example of a icosahedral virus
adenovirus
what is the capsid made of
subunits called capsomers
what are the two main capsid shapes
helical
icosahedral
where is the viral envelope originally from, what do the viruses add to this
previous hosts (lipid bilayer from the host envelopes the virus as it leaves the cell via endocytosis)
viruses encode there own viral glycoprotein genes (e.g. spike proteins)
which type of envelope is more susceptible to harsh environments
the lipid envelope
what enzyme helps phages to enter the cell
lysozyme = weakens the cell wall at the point of attachment
describe the replication cycle of a virus from the point the genome is inside the cell
- host DNA compartmentalised in a nucleus
- viruses with ssRNA form ds intermediate which can be used for mRNA synthesis
- transcription and translation occurs using host machinery
- assembly of new virus particles in the nucleus
- host plasma membrane is taken by new virus = pinches off by budding
where does replication and assembly occur for poxvirus
in the cytoplasm
what occurs in the eclipse period
cell contains viral components - but no complete particles
